Heat treatment of metal-coated glass fibers



A ril 7, 1959 H. B. WHITEHURST 2,880,552

HEAT TREATMENT OF METAL-COATED GLASS FIBERS I Filed Aug. 16, 1954 v 3 Sheets-Sheet 1 /1.9 Fig;

' IN VEN TOR. HARRY B. WHITEHUEST Arron/Ens April 7, 1959 H. B. WHITEHURST HEAT TREATMENT OF METAL-COATED GLASS FIBERS Filed Aug. 16. 1954 3 Sheets-Sheet 2 Q/I/Q INVENTOR.

April 7, 1959 H. B. WHITEHURST 2,

HEAT TREATMENT OF METAL-COATED GLASS FIBERS Filed Aug. 16,

3 Sheets-Sheet 3 Y Big-.1

ATTORNEYS United States Patent HEAT TREATMENT OF METAL-COATED GLASS FIBERS Application August 16, 1954, Serial No. 449,966

4 Claims. (CI. 49-77) This inventment relates to heat treatment of metalcoated fibers and more particularly to electrical heat treatment of metal-coated glass fibers to increase their wearability and breadth of use.

With the ever-widening adoption of glass fibers for use'in products where their high-strength properties are utilized, a need has arisen for overcoming or compensating for the relatively low resistance to abrasion of such'fibers in some applications. In this respect,metal coatings on glass fibers have been found capable of greatly increasing their abrasion resistance properties. Various metals and alloys of metals may be applied to glass fibers'for this purpose. Metal such as copper, zinc, lead, tin, aluminum, silver and steel have been so applied, and alloys such as zinc-titanium, tin-lead, brass, bronze and others canalso be applied. To gain thefull advantage of the metal coatings, however, many specific uses dictate 'theneed for treatment'of themetal after application to the glass to obtain certain desired characteristics or optimumin properties that can be provided by the metal used.

' In general, .the heat treatment of metals for desired properties entails reheating the metal after application, and then controlling the rate of cooling according to predeterminedpatterns orcycles which add'to the thermalhistory of the material to produce the desired predeterminable properties. The controlled cooling may be accomplished by such means .as quenching in oil or water or gradually reducing 'the temperature Within an oven from a heated or reheated state. .Desired properties mayal'sobe obtained by tempering orby normalizing the metal, both of which entail .reheat and cooling ofithe'metal in an'oven or in air. Among .the pertinent metal'properties which may be improved by such treatment 'are hardness, tensile strength, impact toughness, brittleness, workability, etc.

"Oneof the principle difiiculties entailed in heat treatment of metal-coatedfibers, however, is that all too frequently an over-heating of the glass occurs at the ternperatures necessary 'to obtain the desired properties in metal.

On being overheated, the strength properties of glass are greatly reduced to a point where the advantages of the glass surrounded by the metal are lost for many applications where the fibers would otherwise prove highly desirable. Glass in'the form of fibers or filaments may be reheated totemperatures in the neighborhood .of 400 to 700 F., dependent upon the specificglassused, without :detrimentally affecting strength properties, but areheat" to temperatures as high as 1800"F. as is frequent- Iy required to effect heat treatment of-metal for desired properties, substantially reducesor eliminates the strength advantage of the fibers.

Ac cordingly, his a principle object of the present invention to controllably impart predetermined physical ice ment of the metal without detrimentally aifecting the'desirable strength properties in the glass.

It is another object-of the present invention toprovide a method and means for controllably effecting heat treatment of metal coatings'on glass fibers to obtain'optimum characteristics while still retaining the desired properties in the glass. '7

A still further object of the invention is to provide a simple and economical method for heat treating the metal coating of glass fibers adaptable to conventional fiber-forming processes.

These objectives are attained according to the present invention by separately and rapidly heating the metal of the coated glass fibers to desired temperatures to-e'ffeet crystalline rearrangement within the metal'before the glass has an opportunity to receive appreciable amounts of heat. In this respect, the thinner, the coating of metal, the smaller is the amount of thermal "energy required to raise the metal to treatment temperatures, and correspondingly the lesser is the likelihood that the total amount of heat in the metal will be sufficient to raise the temperature of the glass appreciably.

Separateheating of the metal to the high temperatures required for the properties desired can be accomplished according to the invention by utilizing the electrical'conductivity of the metal to heat the metal alone. To eifect such electrical heating, the coated glass fibers may'be passed through an electromagnetic field within which the metal is virtually flash heated. The metal can'be heated by high or low-frequency currents induced therein on passage through a field generated by an inductive type transducer, and under suitable conditions the metal coating about the individual fibers may be used as a closed loop forming in effect the secondary circuit-of a transformer. Extremely high currents can thusbe induced in .themetal coatingsto rapidly raise the temperature of thin metal coatings without producing sufiicient heat'to raise thetemperature'of the glass itself to damaging magnitudes.

.Inotherinstances the metalmay beheated by direct current passed locally through the coatings. In still other arrangements, thin coatings may be flash heated properties to .tnetal-coate'd glass fibers by heat treatby'direct application of flames directed locally overtthe coating surfaces tosupply .heat .at a rate sufficient to raise the temperature of the'metal without appreciably affecting the temperature of the glass encasedtherein.

.A feature of the present invention is thatmetal-coate'd fibers can be provided with a much greater degree of wearabilit-y than was heretofore possible while still retaining the desired tensile and flex properties of :the glass.

Another feature lies inxthe fact that certain metals can :be used to advantage in :the coating ofglassfibers which except for the present invention could not be utilized.

.A .still further feature lies'in the fact that heat treatment :of the coating may be effected by high-speed means adaptable .to high-speed fiber-forming and coating operations.

Other objects and ifeatures which :I believe to "be characteristic :of .myinvention are set vforth with :particularity in :the appended claims. My invention, however, vboth :in .organization and manner of construction together with further objects and advantages thereof may be best understood by reference to ztheifollowingdescription .taken in connection with the accompanying drawings, "in which:

Figure lis a general layout of apparatus for tinuous production of metal-coated .glass fibers .in .which :1 schematically illustrated coil .is .used to inductively heat Qthe metal of the. fibers;

Figure 2 is a front-elevational view of the apparatus shown in Figure 1;

Figure 3 is a perspective view of another unit by which the metal of the fibers may be inductively heated;

Figure 4 is a view in perspective of electrical means by which heating currents may be caused to flow conductively through the metal of the glass fibers;

Figure 5 is a view in perspective of means which cause the heating currents both to be induced and conducted through the metal coatings;

Figure 6 is a somewhat schematic view of an arrangement for flash-heating the metal of coated fibers by flame means; and

Figure 7 is a side-elevational view of another arrangement of apparatus for continuously producing metal-coated glass fibers and for simultaneously heat treating the metal by a multi-stage treating process.

Referring to the drawings in greater detail, apparatus for continuous production of metal-coated fibers, as illustrated in Figures 1 and 2, incorporates a source of molten glass such as a melting furnace having an associated bushing or feeder 10 from which molten streams of glass are fed through orifices 11 to be attenuated into continuous filaments or fibers 12. The spaced fibers are gathered together on passage over a suitable gathering member such as a shoe 16 made of material such as graphite which is compatible with the surfaces of the fibers contacted and is capable of withstanding relatively high temperatures. The force for attenuation of the fibers is provided by a winder 20 having a rotating collet on which a forming tube 22 is mounted and driven for collection of the strand 10 into which the fibers are gathered. The strand 19 is collected into package form on the tube 22 in accordance with a traverse pattern effected by a traverse such as a multi-spiral wire traverse 21.

Metal coatings are applied to the glass fibers 12 from an applicator unit 13 from which metal in a molten state is fed to the glass fibers at suitable points below the feeder orifices 11 where the temperature of the fibers are appropriate for receipt of the metal as a coating in integral and uniform relationship with the glass. It should amount to raise the temperature of the glass an appreciable degree. In such instances the volume of metal raised in temperature is so small in comparison to the volume of glass, that even if all the heat in the metal were to be transferred to the glass, only a small rise in temperature of the glass would occur.

The heat tending to move from the coating material toward the interior of the fibers is transferred by conduction whereas the heat removed from the metal coatings to the exterior is effected by convection and radiation. The fact that the exterior or outer peripheral surface of the metal coatings is greater in area than the interfacial surface of the metal and glass enhances the tendency of heat dissipation from the exterior surface. Additionally, the rapid rate of movement of the fibers increases the rate of removal of heat by convection currents since in moving through a mass of air, the fibers generate a turbulent convection condition about themselves.

Thus, it will be seen that the metal of coated glass fibers may be heated to a heat-treating temperature at an extremely rapid rate and cooled at a correspondingly rapid rate without appreciably raising the temperature of the glass surrounded thereby.

The power supply to the induction coil may be an MG set having a frequency falling within the range of 2,000 and 10,000 cycles per second or may be a conventional electronic tube oscillator, or mercury arc oscillator capable of high frequencies, and in some instances may be spark-discharge oscillator capable of producing frequencies up to and in the range of 500,000 cycles per second. The coil 23 energized by such currents is suitably cooled such as by forming it of copper tubing and not shown. Under certain circumstances, the sizing fluid be noted in this respect that the molten glass on emission from the orifices 11 is rapidly reduced in temperature and that the metal emitted from the orifice 14 in the applicator unit 13 is arranged to be applied at predetermined desired points on the fibers where the temperature corresponds to that which will provide the desired properties in the coated material within the range of properties obtainable by positioning of the applicator for the temperature of the metal being applied.

After cooling and solidification of the metal coatings on the fibers, and while still in spaced relationship before being gathered into a strand, the coated fibers are passed through an induction coil 23 to have heating currents induced therein to reheat the metal. The energy input to the coil may be supplied by a power supply 24 of conventional type while the orientation of the coated fibers is such that the coatings in effect form tubular or short-circuited secondary loops about each of the glass filaments which aids in heating the metal at an extremely rapid rate to the temperature desired before the heat has an opportunity to penetrate the glass core to raise it to a damaging strength-reducing temperature. In this respect, it should be noted that the metal coatings, even though supplied from a source located on one side of the fibers, completely envelop the fibers to form a casing thereabout.

The thiickness of the coatings may range from molecular dimensions to about 50% of the diameter of the fibers and up. In many instances when the thickness is a minor percentage of the total diameter of the individual fiber, however, the heat generated in the coating to raise the temperature to heat-treating magnitudes, is insuflicient in can be utilized to advantage as a quenching fluid for high temperature metal coatings. In this respect, the sizing fluid would rapidly reduce the temperature of the coatings in addition to performing the usual sizing functions of imparting lubricity and integrity to the mass of gathered filaments.

Figure 3 shows an electromagnetic yoke-type induction-heating unit for inducing electrical heating currents in the metal of coated glass fibers. The magnetic yoke or core 31 of the unit is a longitudinal, generally U- shaped laminated structure of magnetic material in which flux concentration is built up by a coil 31 wound upon a back leg 35. Alternating current energy is supplied to the unit by a suitable alternating current supply source 34.

Metal-coated fibers 32 are drawn over the gap formed between two forwardly extending legs 36 and 37 of the unit between which flux buildings up and collapses alternately in accordance with the frequency of the powersupply source. Energy losses accordingly occur in the metal coatings of the fibers for generation of heat as the filaments pass over the gap between the two legs. Heat energy is developed in the metal coatings by eddy current losses, as well as hysteresis losses in the case of magnetic materials such as steel. When the coatings are made of non-magnetic material such as copper or brass, however, the heat developed in each coating is due principally to eddy current losses.

Figure 4 shows another method and means whereby the metal coatings and fibers may be heated by current passed directly therethrough between two electrodes making contact with the fibers in their passage from the metal eoater to the gathering shoe. The metal-coated fibers 42 are passed over a pair of suitably mounted spaced parallel rod-type electrodes 45 and 46 made of electrical-conduction temperature-resistant material such as graphite. The electrode material must also be of a nature which .is compatible with the contacted :coating material drawn thereover. The electrodes 45 :and A6 .are connected to an electri "al power source -.44 :from which the electrical current is supplied for passage .over the length of the moving fibers contactingand bridging the electrodes. Although the electrical energy supplied to the metal coatings in this instance may be of highfrequency character, it may also be of low-frequency or direct-.current-icharacter 'in lview .ofthe :fact that the current is conducted directly through the metal coating on the glass fibers rather than being induced therein. The spacing between theelectrodes '45 and 46 can be adjusted to cause the current flow to extend over a length of fibers 42 corresponding to the time required to bring the'coatings up to desired temperature for the period necessary to effect the'desired treatment.

Figure 5 shows another electromagnetic induction unit in which heat is generated in the metal of coated glass fibers by currents which are both induced therein and conducted therethrough. -Current is induced in'the metal coatings by a magnetic core 51 having a winding 53 wound about its back leg 59. The yoke is generally lJ-shaped ancl is of a width dimensionsuflicient to extend across the width of the number of spaced metalcoated-fibers to-be heated. The fibers 52 traverse the gap between the two forwardly extending legs 57 and 58 of the core and are held in a plane generally parallel and slightly in front of the face of .thelegs .by apair of electrodes 55 and 56 which bridge the gap formed between the legs 57 and 58 and which are insulated therefrom by suitable insulating separators 60. The electrodes are made of heat-resistant, electrically-conducting material such as graphite which is also compatible with the material contacted. Energy for the coil 53 is supplied by a power unit 54 which also may be utilized to supply energy to the electrodes 55 and 56. On passage over the electrodes, the fibers 52 have electrical energy induced therein by reason of the build-up and collapse of the magnetic fields emitted from the yoke 51, but in addition, currents are passed through the coatings by conduction from the electrodes 55 and 56 which are connected to an electric power source 64 as in the embodiment of Figure 4. Thus, induced energy and conducted energy are translated into heat energy within the metal coatings on passage over the electrodes, to permit a more rapid and flexibly controllable manner of introduction of heat into the metal coatings. If desired, the heat generated in the metal from the electrodes 55 and 56 may be developed by direct-current energy rather than the alternating current energy supplied by the power unit 54. In this respect, a separate direct-current source may be utilized or a portion of the output of the unit 54 may be rectified for the supply of direct-current energy.

An alternative method by which heat treatment of metal, of coated fibers may be accomplished as illustrated in Figure 6 wherein longitudinal gas burners 63 spaced in staggered relationship on opposite sides of a row of fibers 62 cause flames 64 emitted from the burners to impinge the coatings of the fibers for treatment. The heat of the flames is arranged to be supplied to the metal coatings with sufficient rapidity that the coatings rise in temperature at a much more rapid rate than the rate of rise of the temperature of the glass encased therein. The coated fibers are then rapidly reduced in temperature before the temperature level of the glass reaches a damaging value by quenching them in fluid such as oil, or by merely providing suflicrent linear speed to the fibers to produce an air quench. It will be recognized that as in the embodiment of Figures 1 and 2, wherein the inductive heating coil may be extended in dimension or associated with other coils distributed over the length of the fibers to effect heating over a longer time period, the present arrangement has the advantage that a plurality of closely spaced burners it? may :be -provided -.alon g-the length of the;fibers :62 :to ,provide .a h corresponding :Ionger period of :heating .for .each portionofthecoated fibers. .Byutilization'of this method, the surface of-coatings .such ,as steel may .be flame hardened .to pro'duceextended strength properties in the glass fibers.

Figure 7 shows another arrangement of apparatus for producing metal-coated fibers in which the heat treatment .of the metal may be extended over alonger cycle by the'utilization of a secondary heating oven. The glass fibers 72 attenuated fromthe feeder 7-1 are coated by drawing them over a metal-applicator unit 73. At a distance below the points of application, .the coating metalis reheated by any of-the-methods herein described such as by direct'conduction of heat over a length thereof from electrodes and 86 supplied with electrical energy from a power-supply unit 84. The fibers are subsequently gathered-together at'the gathering shoe 74 into a strand 79 whichis immediately introduced into a secondary heatingoven :maintained at a temperature below that at which the glass may be safelylmaintained without 'detrimentally affecting the strength properties thereof. The length of the oven is made such as to provide the heat treating-temperature desired for azlength .of timenecessary to produce the properties desired to beimpartedto'themetal. :Thus, the reheat of'the metal is effected by the electricalmeans to the hightemperature intended without appreciably raising the temperature of the glass, whereas the secondary oven extends the; period of cooling of-.such metalover the period often found necessary to impart certain properties thereto. After leaving the oven, the strand 79 is wound in usual fashion on a winder 80.

The secondary oven may be provided with an internal atmosphere of carbonizing gas to effect carbonization of metal such as steel, or may contain ammonia gases for nitriding the metal. In utilizing the subsequent reheating or heat treating components in this manner, a real equilibrium may be restored in the metal subsequent to application of the metal under conditions such as may be required to effect the greatest integrity and uniformity on the glass surfaces. The metal can thus be carried toward a real equilibrium away from unstable conditions which might exist by reason of special conditions of application. In general, the fundamental reaction involved in such treatment is one of precipitation and sometimes submicroscopic.

Although the metal-coated glass fibers have herein been shown and described in relation to treatment while in a continuous forming process, it will be understood that the same principles can also be used in a separate operation. Additionally, it will be understood that while the diagrams and explanations have been made relative to treatment of spaced filaments, heat treatment may also be accomplished While the filaments are in strand form.

Thus, while I have shown certain particular forms of my invention, it will be understood that I do not wish to be limited thereto since many modifications may be made within the concepts of the invention, and I, therefore, contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

I claim:

1. The continuous method of producing abrasion resistant high strength metal-coated glass fibers in which the metal is heat treated at an elevated temperature which would normally be effective to substantially reduce the strength of the glass fibers comprising attenuating continuous fibers of glass from a molten body of glass, coating each of said newly formed fibers individually with a continuous complete coat of said metal, heating the metal coat of each individual fiber to said elevated temperature by moving the coated fibers through a heating zone, regulating the heat imparted to the metal coatings in said zone and the speed of the fibers therethrough to raise the temperature of only the metal on the fibers to said elevated treating temperature, and then cooling the metal coatings below said elevated temperature sufiiciently rapidly after such heating of the metal that the glass of the fibers will be maintained below values which would substantially reduce the strength of said fibers.

2. The method of producing a high strength abrasion resistant, glass textile strand comprising continuously drawing a multiplicity of fine glass fibers from a supply body of molten glass, simultaneously and continuously grouping the fibers at a point below said body in the form of a strand, coating each of said fibers individually with metal in a region below said body but above said grouping point where the temperatures of said metal and fibers are such that the high strength of the newly formed fibers is retained, allowing said metal coating to cool in a zone following the coating region, heat treating said metal-coating at an elevated treating temperature for improved surface abrasion resistance by moving the coated fibers through a heating zone following said cooling zone to reheat said metal, regulating the heat imparted to the metal in said heating zone and the speed of the fibers therethrough to raise the temperature of only the metal on the fibers to said elevated treating temperature, and then rapidly cooling the metal coating below said elevated temperature before grouping said fibers such that the glass will be maintained below values which would substantially reduce the strength of said fibers.

3. The process of claim 2 wherein the reheating of the metal coated on the glass fibers is accomplished by causing electric current flow therethrough in the heating zone.

4. The method of claim 2 wherein the cooling of the metal in the heat treatment thereof is done in an atmosphere of controlled composition.

References Cited in the file of this patent UNITED STATES PATENTS 482,879 Purdy Sept. 20, 1892 1,098,794 Fleming June 2, 1914 1,765,520 Adams June 24, 1930 2,030,695 Erber Feb. 11, 1936 2,226,871 Nicholas Dec. 31, 1940 2,234,986 Slayter et a1. Mar. 18, 1941 2,373,078 Kleist Apr. 3, 1945 2,405,037 Hsu July 30, 1946 2,437,776 Wilson Mar. 16, 1948 2,502,770 Watson Apr. 4, 1950 2,584,763 Waggoner, Feb. 5, 1952 2,616,165 Brennan Nov. 4, 1952 2,772,518 Whitehurst et a1. Dec. 4, 1956 2,782,563 Russell Feb. 26, 1957 Brown and Associates: Unit Operations, John Wiley and Sons, 1950, page 426.

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